1. Field of the Invention
The present invention relates to telecommunications and, more particularly, to a method and system for broadcasting or multicasting a message to a specific group of mobile stations in a cellular wireless communications system.
2. Description of Related Art
The advent of wireless telecommunications, such as cellular telephony, has extended the functionality available to wireless users: Just as a user can operate a cellular telephone or other mobile station (MS) to place a voice call to virtually any telephone number, a user can also operate a suitably equipped MS (such as, for example, a web-enabled wireless telephone) to place a data call to virtually any remote computer. Once such a connection is established, a remote computer can send data to the MS, much as a remote computer might send data to any personal computer connected to the Internet.
In a typical cellular radio communications system (i.e., a wireless telecommunications network), an area is divided geographically into a number of cell sectors, each defined by a radio frequency (RF) radiation pattern or air interface from a respective base transceiver station (BTS) antenna. A number of MSs (such as cellular telephones, personal digital assistants (PDAs) and/or other devices) may operate concurrently in a given cell sector, all communicating via the air interface with a common BTS. In turn, the BTSs from a number of cell sectors may communicate concurrently with a common base station controller (BSC), which may function to aggregate and control traffic for the multiple BTSs. A number of BSCs may then communicate concurrently with a common gateway, such as a packet data serving node (PDSN) or mobile switching center (MSC), which may function to set up and connect communications to or from other entities. The BTS, BSC and gateway, in combination, comprise a radio network that provides network connectivity for an MS.
Generally, a user's MS is allocated a dedicated channel over which data may be sent and received. However, there are a number of specialized services that multiple wireless customers may find desirable. Examples of services that may be sent to multiple users could include:                Location-based advertising;        Vertical services, maintenance, and administrative messages        Public information services, such as sports scores, traffic conditions, weather alerts, etc.;        Video clips of newsworthy events; and        Audio and video streaming.        
In some specialized services, a number of MSs in a cell sector (or even all customers in the cell sector) would receive the same message. This does not present much of a problem when only a few users are to receive the data, but can tax a network's capacity as more users receive the same message. One resource that can be taxed is the air interface. The air interface between MSs and the radio network is a scarce resource, and its use should be conserved whenever possible. In addition, as high-bandwidth applications become more commonplace, the capacity between other entities and links in wireless communications networks may also be taxed. As an example, if a BTS is to support a number of concurrent high-bandwidth communications with multiple MSs, the link between the BTS and the BSC must support all of that traffic at once.
The link between a BTS and BSC, though, is typically a transmission line with a finite bandwidth. Similarly, the link between the BSC and a gateway such as a PDSN or MSC is typically a transmission line with finite bandwidth. Of course, it is possible to increase traffic capacity between various network elements by simply adding more transmission lines. Adding transmission lines, though, can be very expensive, since it requires a provider to either physically add the lines, or to lease additional lines from a local exchange carrier (LEC). Leasing lines from LECs to increase the traffic capacity between network elements can, in fact, be a significant portion of a cellular provider's total operating cost.
Thus, when a particular message (especially, but not necessarily, one requiring a significant amount of available bandwidth) is to be sent to a relatively large number of MSs within a cell sector (or to multiple cell sectors), a system for transmitting the message that conserves the cellular system's bandwidth is a significant improvement over a multicast system that transmits messages to cell sectors indiscriminately. Moreover, it would also be desirable to control which users have access to specialized services so that users who want such services can be required to pay for them, and also so that users who do not want the services are not bothered by unwanted messages.